1. Field of the Invention
The present invention relates in general to computers, and more particularly to apparatus, method and computer program product embodiments for dynamically comparing volumes for asynchronous remote copy verification.
2. Description of the Related Art
In enterprise data processing arrangements, such as may be used in a company, government agency or other entity, information is often stored on servers and accessed by users over, for example, a network. The information may comprise any type of information that of programs and/or data to be processed. Users, using their personal computers, workstations, or the like (generally, “computers”) will enable their computers to retrieve information to be processed, and, in addition, to store information, for example, on remote servers.
A computer network of a business may have multiple storage networks that are located remote from one another and a business user. The storage networks may also be hosted on different types of systems. Such storage networks may be useful for clients, for example, to establish a redundant source of data in event of a failure of the primary storage system. Disaster recovery techniques that can tolerate the failure of a complete data center have become increasingly important. A classical technique used for tolerating data center failures is copying the data to a remote site. This technique is known as remote-mirroring. There are various forms of remote-mirroring. They can primarily be classified as either synchronous or asynchronous. Synchronous remote-mirroring techniques delay acknowledging an I/O to a host until it has been executed on the remote site as well. Asynchronous techniques, on the other hand, acknowledge an I/O as soon as it executes on the primary site.
Synchronous remote-mirroring techniques usually have high impact on I/O performance, high bandwidth requirements, zero data loss, and very small time to recovery. Asynchronous remote-mirroring techniques usually have low or no impact on I/O performance, low bandwidth requirements, possibility of data loss, and higher time to recovery. Asynchronous mirroring techniques can be classified further along two dimensions, including write-ordering and write-coalescing. Write-ordering is focused on maintaining the order of writes at the remote mirror. Write-coalescing is focused on coalescing multiple writes to the same block (at the mirror) into one write. Write coalescing reduces bandwidth requirements when write-locality exists.
Clients who use remote mirroring functionality of their disk storage for disaster recovery may wish to verify that the copy of the data is correct. Traditionally, such verification is performed by comparing data between the “primary” volume and “secondary” volumes.